6.3 Analysis Flashcards
What are the two deuterated compounds in NMR spectroscopy
CDCl3
D2O
What is the role of CDL3 in NRM spectroscopy?
used as a solvent
What is the role of D2O in NMR spectroscopy
used to identify OH OR NH
protons
What is the stationary phase in chromatography?
Whatever is fixed in place: may be gel, paper, liquid
What is the mobile phase in chromatography?
Moves in a definite direction: could be gas or liquid solvent.
What can TLC be used for?
To check the purity of a substance
To check a reaction has fully occurred
What is retention time?
Time taken for component to travel from the inlet to the detector in gas chromatography.
On an absorption time graph, what is the area underneath the peaks equal to?
Concentration
What test for alkenes (unsaturation)?
Bromine water
Orange to colourless?
What test for haloalkanes?
Silver nitrate and ethanol
White ppt: chloroalkane
Cream ppt: bromoalkane
Yellow ppt: iodoalkane
What test for carbonyl?
2-4,DNP (Brady’s reagent)
Forms a yellow orange ppt
What test for aldehydes?
Tollen’s reagent
Silver mirror
Fehling’s solution
dark red ppt
Acidified dichromate:
orange to green when refluxed
What test for carboxylic acids?
Reactive metal or carbonate:
Will cause effervescence
What test for phenols?
Will not react with carbonates
What test for alcohols?
Reflux with acidified potassium dichromate
orange to green
What is TMS?
Internal standard for both carbon and proton NMR.
It creates the chemical shift axis and is given the value of 0 for all other compounds to be compared to.
Why is TMS a good internal standard? (5 things)
-Contains both carbon and hydrogen so can be used for both types of NMR
-Produces one sharp signal all all hydrogens are in the same environment, only one carbon so only one peak in carbon NMR
-Non-toxic
-Low b.p and volatile so can be removed from sample
-Inert so unlikely to react with sample being analysed
Why can’t benzene or TMS be used as solvents?
They contain carbon and hydrogen so would produce peaks.
What was CDCl3 before it was deuterated?
CHCl3
Describe D2O
It has the same structure as water but uses the H2 isotope
How is D2O used in proton NMR?
-proton NMR spectrum is run
-small amount of D2O is added to sample (vigorous shaking as D2O and CDCl3 are immiscible)
-second proton NMR is run, any peak due to -OH or -NH is removed
Why does D2O work?
A deuterium substitutes a H
CH3OH + D2O -> CH3OD + HDO
What can we say about the splitting of -OH and -NH?
The protons are not split, they usually show as broad singlet peaks.
Why are -OH and -NH signals broadened?
Because it’s hard to get completely dry solvents. Traces of water form H bonds with -OH and -NH protons in the compound.
